This can be done with any character as long as the person you are
telefragging is on your own team. When you go up to revive sum1,
immediately after you revive them press Crouch to telefrag them.
*** You will lose points.

When playing as the Tech online, switch to your grenade launcher and
use your primary fire on an enemy turret to easily take it out. This
also works on enemies, but not as well. Also, if there is a room
with people crowded inside, use the secondary fire with your grenade
launcher to gas them all. Fire about 2 shots in the room to take
them out.